Many different cutting techniques have been developed for cutting tissue paper. For example, there is a conventional roller-type straight-knife cutting mechanism consisting of an inline knife and a roller. In a paper cutting operation, a long tape of paper to be cut is wound around the roller, and the roller is caused to continuously rotate while the knife reciprocates vertically corresponding to the rotating roller. When a cutting edge of the knife contacts with the roller, the paper is cut.
However, during the conventional paper cutting operation, the cutting edge of the knife and the long tape of paper wound around the roller are in line contact with each other. At the instant of contact, the cutting edge of the knife bears a considerably large normal or angular contact force and therefore tends to break easily.
In the existing tissue paper cutting techniques, a cutting manner based on the shearing principle by using an upper knife and a corresponding bed knife roller has been widely employed. Most currently very common tissue paper cutting mechanisms include a one-piece oblique knife, a compound oblique knife, or a simple spiral curve knife as the upper knife thereof. When cutting paper with these types of knives, they either bear an uneven contact force or contact with the bed knife roller at multiple contact points at the same time. As a result, not only the upper knife, but also a knife carrier thereof and the bed knife roller would bear a relatively large or uneven impact at the instant of contact to become deformed or damaged and therefore have a largely reduced usable life.
FIG. 1 schematically shows the motion relation between a compound oblique upper knife N1 and a straight bed knife N2. As shown, the oblique upper knife N1 contacts with the straight bed knife N2 at multiple contact points at the instant of cutting, and the upper knife is subjected to relatively large impact and vibration.
Paper cutting mechanisms with one-piece oblique upper knife or simple spiral upper knife and straight bed knife have been developed in an attempt to overcome the drawbacks of the paper cutting mechanism with compound oblique upper knife and straight bed knife. FIG. 2 schematically shows the motion relation between a one-piece oblique or a simple spiral upper knife N3 and a straight bed knife N4. As can be seen from FIG. 2, while the oblique upper knife N3 contact with the straight bed knife N4 at only one contact point at the instant of cutting, the oblique upper knife N3 is fed at a relatively quick speed and is still subjected to a relatively large impact and vibration.